Electromagnetic device for circuit breaker trip unit assembly



April 7, 1970 H. R. SHAFFER v 3,505,626

ELECTROMAGNETIC DEVICE FOR CIRCUI-T BREAKER TRIP UNIT ASSEMBLY FiledJuly 11, 1968 I s Sheets-Sheet i April 7, 1970 H. R. SHAFFER 3,505,626

ELECTROMAGNETIC DEVICE FOR CIRCUIT BREAKER TRIP UNIT ASSEMBLY Filed July11, 1968 v a Sheets-Sheet 2 April7, 197O H.R.SHAFF R r '3,5o5,62s

ELECTROMAGNETIC DEVICE FOR CIRCUIT BREAKER TRIP UNIT ASSEMBLY Filed July11, 1968 8 Sheets-Sheet 3 B Y dsmalgvz, 51554: 6598 j 53? April 7, 1970H. R. SHAFFER ELECTROMAGNETIC DEVICE FOR CIRCUIT BREAKER TRIP UNITASSEMBLY Filed Julyll, 1968 8 Sheets-Sheet 4 INVEAW'OR HUM/4Z0 5/44/7 52M Z (A 3% April 7, 1970 R. SHAFT-ER 3,505,626

ELECTROMAGNETIC DEVICE FOR CIRCUIT BREAKER TRIP UNIT ASSEMBLY Filed July11, 1968 s Sheets-Sheet 5 Z67 E3 'I Jr ca 74 A524 Eli/55A April 7, 1970H. R; SHAFFER 3,505,625

ELECTROMAGNETIC DEVI ICE EOR CIRCUIT BREAKER TRIP UNIT ASSEMBLY FiledJuly 11,- 1968 8 Sheets-Sheet e flaw/ea ,7. 97/4/55? IJ'TeaL 5/1/46595:3, fees 2124a AP 7, 1970 I 1 H. R. SHAFFER' 3,505,626

ELECTROMAGNETIC DEVICE FOR CIRCUIT BREAKER TRIP UNIT ASSEMBLY Filed July11, 1968 s Sheets-Sheet v .fil/A/" F025;

I 350 R 6 40-- 3 Q flew/702E fia5/r/d/v .F-JEZ AZM/WY/FE faea K 522/;F026: 350 xx/0W 4 .f/F/A GZ? Fae Cf (am/65s) J sca (4) April 7, 1970 IH. R; SHAFFE R v 3, 0 6

ELECTROMAGNETIC DEVICE FOR CIRCUIT BREAKER TRIP UNIT ASSEMBLY Filed July11, 1968 I s Sheets-Sheet 8 EEZ4 .JEEiJS- B Y QFTQULEAJKI Fr es/q Qseflpeh United States Patent ()1 3,505,626 Patented Apr. 7, 197

3,505,626 ELECTROMAGNETIC DEVICE FOR CIRCUIT BREAKER TRIP UNIT ASSEMBLYHoward R. Shalrer, Glenside, Pa., assignor to I-T-E ImperialCorporation, Philadelphia, Pa., a corporation of Delaware Filed July 11,1968, Ser. No. 744,166 Int. Cl. H01h 9/00 U.S. Cl. 335-176 23 ClaimsABSTRACT OF THE DISCLOSURE An electromagnetic device of the type havingapplication for a circuit breaker trip unit assembly, utilizing amodified armature biasing structure as Well as a means for indicatingactuation of an individual magnetic assembly. The modified armaturebiasing structure provides a decrease of the force urging the armatureaway from the cooperating pole faces, as the armature gas separationdecreases. By avoiding the heretofore practical arrangement ofincreasing the bias force with a reduction of the gap separation, thedisclosed structure permits a wider range of operation. The visualindicating means in conjunction with the trip unit assembly serves toreadily indicate to the operator which pole of a multi-phase device hasbeen actuated and will require manual reset.

The above noted features may be combined, and in onesuch combinedarrangement, the armature bias force is reversed at the concludingportion of its travel, to lock the armature against the magnet polefaces until manually reset.

My invention relates to improved electromagnetic devices, havingapplication in conjunction with circuit breaker trip unit assemblies.

In accordance with one aspect of my invention, the biasing forcesupplied to the armature of the electromagnetic structure is reducedduring at least a portion of its movement towards the magnet pole faces.Although the ensuing discussion is directed to such a circuit breakerapplication, it should naturally be understood that this concept is notlimited to circuit breakers, and such a negative force gradientcharacteristic device will have utilization in other applications,wherein it is desired that the armature biasing force does notprogressively increase as the armature member approaches the cooperatingmagnetic pole faces.

In accordance with another aspect of my invention, a visual indicatingmeans is provided to indicate actuation of the electromagnetic trip.This visual indicating means, once set responsive to magnetic actuation,will remain in this condition until manually reset. Such a visualindicating means advantageously permits the operator to distinguish froman overload fault and an instantaneous fault when a circuit breaker hastripped, and to advise the operator which of the phases of a multiphaseunit has experienced the fault condition.

The invention is shown in conjunction with a circuit breaker trip unitassembly of the general type, and having application in the circuitbreaker device shown and more fully described in U.S. Patent No.3,319,195 issued May 9, 1967 in the names of Albert Strobel and John C.Brumfield, based on an application filed June 21, 1965 and assigned tothe assignee of the instant invention. As shown therein, such automaticcircuit breakers are usually provided with a trip unit assembly whichincludes an overload magnetic trip instantaneously responsive to asevere overload condition. The trip unit assembly may also include athermal trip assembly responsive to a more moderate, but sustainedoverload condition. The instantaneous trip assembly, to which theinstant invention pertains, includes a stationary magnet member and acooperating armature member. A biasing means is provided to urge thearmature away from the magnet, such that in the absence of apredetermined fault condition the energization of the magnet member willbe insufiicient to overcome the biasing means and move the armaturetowards the magnetic pole faces. The instantaneous trip unit assembly isadjustably calibrated in accordance with the bias force and the initialair gap separation, such that upon the occurrence of a particular faultcondition, the magnetic energization will be sufficient to overcome thebias force and thereby move the armature towards the magnetic polefaces. This armature movement causes the rotation of a tripping bar, andthe associated release of a latch mechanism in conjunction with thecircuit breaker operating mechanism for follow-up movement of thecircuit breaker contacts to their tripped open position.

In past trip unit assemblies, as typified by U.S. Patent No. 3,319,195,the armature biasing means is associated with the armature movement, 'ina manner that will increase the biasing force as the armature movestowards its magnetic pole faces. This disadvantageously requires themagnet to operate against an increasingly greater spring bias force asthe armature is moved towards the pole faces. Further, the need toprovide an increasing portion of the magnetic force to overcome thearmature bias spring results in a lesser force being available at thetripper bar.

Further, in such circuit breaker trip unit assemblies, it is generallyrequired to include an instantaneous trip adjustment for selecting themagnet pickup point over a predetermined range. This permits a singletrip unit assembly to have application for a range of circuitconditions, with the user selecting the desired pickup point inaccordance with the circuit demands. Such a trip unit adjustment may beof the type shown in U.S. Patent No. 3,302,140 issued Jan. 31, 1967 inthe name of Albert Strobel entitled Circuit Breaker Instantaneous TripAdjustment, based on an application filed June 21, 1965, and alsoassigned to the assignee of the instant application. As shown therein,and in numerous other trip adjustment structures, the magnet pickuppoint is modified by changing the initial air gap separation between thearmature and the magnetic pole faces. As the armature is moved closer tothe magnet pole faces in the nontripped position, with a lessening ofthe air gap separation, the reluctance of the magnetic path will bedecreased and should require less magnetic energization to draw thearmature towards the magnetic pole faces. Thus, the initial placement ofthe armature closer to the magnetic pole faces is usually associatedwith a lowering of the instantaneous magnetic pickup point. In suchprior art devices, the movement of the armature closer to the magneticpole faces had also been accompanied by an increase in the armature biasforce. This increased armature bias force opposes the desired effect ofreducing the magnetic pickup point. Since the instant invention reducesthe bias force as the armature moves closer to the pole face, the changeof bias force acts in cooperation with adjustment means, rather thanopposed to it, and thereby enhances the operation of the instantaneoustrip adjustment. It has been demonstrated that by virtue of the improvedstructural arrangement of my invention, the trip unit adjustment rangemay be increased by at least 50%, and up to over comparable sizemagnetic structures of the prior art.

In such circuit breaker units, it is normally not possible for theoperator to determine whether tripping has occurred as a result of theactuation of the instantaneous trip assembly, or the overload thermaltrip means. Further, there is usually no way for the operator todetermine which of the phases has experienced the fault. My improvedtrip unit assembly includes, as an additional feature, a means forreadily indicating the actuation of the magnetic trip unit assembly. Inaccordance with one embodiment, such movement is associated by areversal of the armature biasing force, so as to maintain the armatureagainst the magnetic pole faces until manually reset. In accordance withanother embodiment of the invention, the visual indicating means isprovided in conjunction with the trip unit calibration adjustmentbutton. In accordance with the modified structure of the calibrationadjustment button, the movement of the armature downward serves topermit similarly axially downward movement of the calibration button,and it will be maintained in this axially downward position untilmanually reset.

It is therefore seen that the basic concept of the instant inventionresides in providing an improved magnetic structure having utilizationin conjunction with a circuit breaker trip unit assembly. The featuresof the magnetic structure include a negative force gradient in theinterconnection means between the armature and its associated biasingmeans, and a visual indicator for readily apprising the operator ofmagnet actuation.

It is, therefore, a primary object of the instant invention to providean improved electromagnetic device.

Another object of the instant invention is to provide an electromagneticdevice wherein the armature biasing force is reduced as the armaturemember is drawn to wards the pole faces of its cooperating magnet.

A further object of the instant invention is to provide within anelectrical circuit breaker an instantaneous trip unit assembly, in whichthe armature biasing force is reduced as the armature moves closer tothe magnetic pole faces.

An additional object of the instant invention is to provide anelectrical circuit breaker device with an adjustable trip unit assembly,wherein the range of adjustment is increased by at least 50% overcomparable magnetic assemblies heretofore available.

Still another object of the instant invention is to provide within acircuit breaker device a magnetically actuable instantaneous trip unitassembly having a range of adjustment achieved by varying the initialposition of the armature, wherein the initial movement of the armaturetowards the pole faces to lower the magnetic pickup point is accompaniedby an associated decrease of the armature bias force.

Still a further object of the instant invention is to provide, inconjunction with a circuit breaker trip unit assembly including amagnetically actuated fault sensing means, a visual indicating means forapprising the operator of magnetic actuation.

My improved negative force gradient armature biasing means is achievedby an arrangement of levers and springs to provide an effective negativegradient force during at least a portion of the armature movement. In anillustrated embodiment, the interconnection means between the springbias means and the armature includes a pivoted lever which establishes amoment arm for applying the spring force to the armature. As thearmature moves towards its associated magnetic pole faces, the lever ispivoted in a manner to reduce the moment arm of the spring force. Thisreduction of the moment arm is designed to overcome the actual increasedspring force as the spring expands, such that the applied product of thespring force and moment arm will be of lesser magnitude as the armaturemoves towards the magnetic pole faces.

In accordance with a further advantageous feature which has foundapplicability in conjunction with some of the forms of my invention, acounterbalance assembly may be utilized in conjunction with theinterconnection of the spring bias means to the armature. Thiscounterbalance assembly counteracts shock induced movement of thearmature towards the magnet, and has demonstrated particular utility inconjunction with circuit breakers installed in environments which may besubjected to appreciable shock forces, e.g., shipboard use.

It is, therefore, still a further object of the instant in vention toprovide an electromagnetic device having an armature biased away fromits cooperating pole faces, which is counteracted by a negative forcegradient as it moves towards the magnetic pole faces.

Still an additional object of the instant invention is to provide suchan electromagnetic device Within a circuit breaker trip unit assembly,in which the moment arm applying the biasing spring force to thearmature means experiences an effective reduction as the armature movestowards the magnetic pole faces.

Yet another object of the instant invention is to provide such anelectromagnetic trip unit assembly wherein such reduction of the momentarm is accompanied by an increase in spring force, with the resultantproduct being a decreased magnitude.

Yet an additional object of the instant invention is to provide, withinan electrical circuit breaker, an instantaneous trip unit assemblyhaving a negative force gradient in conjunction with the armaturebiasing spring, wherein the moment of the armature force reverses as thearmature reaches the magnetic pole faces, so as to lock the armature inthe trip position and require a manual reset.

These, as well as other objects of the instant invention, will becomereadily apparent upon a consideration of the following description anddrawings, in which:

FIG. 1 is a plan view of a three-phase molded case circuit breakerdevice, utilizing one form of the instant invention, and wherein thecover, and the cover of the trip unit assembly, are partially removed toreveal the region containing the electromagnetic device of the instantinvention.

FIG. 2 is a longitudinal cross-sectional view along the line 2-2 of FIG.1, and looking in the direction of the arrows, showing the center phaseand including the circuit breaker operating mechanism.

FIG. 3 is an end view of the replaceable trip unit assembly, partiallycut away to show the instantaneous trip portion.

FIG. 4 is a perspective view, partially exploded, of the magnetic tripunit assembly constructed in accordance with the instant invention, andutilized in the trip unit of FIG. 3.

FIG. 5 is a cross-sectional view along the line 55 of FIG. 3, showingthe details of the electromagnetic instantaneous trip assembly.

FIG. 6 is a cross-sectional view along the line 6--6' of FIG. 5.

FIG. 7 is a simplified view of a portion of FIG. 5, increased in size,to show the manner in which the moment arm varies as the armature movestowards the magnetic pole faces.

FIG. 7A is a simplified schematic representation of FIG. 7, showing thebasic operation of the device.

FIGS. 8 through 11 show a modification of the general form of magnetictrip unit assembly shown in FIGS. 1 through 7, in which the armature islocked in its final position, and a visual indication is provided, inconjunction with a manual reset means, FIG. 8 is a front elevationalview of the modified trip unit assembly. FIG. 9 is asimplified end viewshowing the device in the tripper' position. FIG. 10 shows the visualindicator in the nontrip normal position. FIG. 11 shows the manner inWhich the spring pivots to provide a reversal in movement for thelocked-in condition.

FIG. 12 graphically represents the spring force and moment of forcevariation, versus armature position, corresponding to the embodiment ofFIGS. 1 through 7.

FIG. 13 graphically represents the spring force and moment of forcevariation versus armature position corresponding to the embodiment ofFIGS. 8 through 11.

FIGS. 14 and 15 show another form of the instant invention, having amodified visual indicating arrangement, in conjunction with theinstantaneous magnetic adjustment button, for indicating actuation ofthe magnetic assembly. HG. 14 shows the non-actuated condition, and FIG.15 the actuated condition.

Reference is initially made to detailed FIGS. 1 through 7, and schematicrepresentation FIG. 7A, which show electromagnetic devices built inaccordance with the instant invention, installed within the replaceabletrip unit assembly of a commercial three-phase circuit breaker, of thetype shown in aforementioned U.S. Patent Nos. 3,302,140 and 3,319,195.It should naturally be understood that the novel concepts of the instantinvention may be incorporated in numerous other types of circuitbreakers or other electrical switching devices, with this detailedembodiment being merely for illustrative purposes.

Circuit breaker 10 is assembled in a housing comprising molded base 11,separated into compartments 12, 13 and 14, respectively, for locatingthe operating members of each of the phases. The adjacent compartmentsare sepa- 20 and load terminal strap 21 is as follows. The line terminalstrap 20 includes at its inward end the main and arcing stationarycontacts 22, 23. With the circuit breaker in the ON condition, thesecontacts are in engagement with cooperating movable contacts 24, 25,respectively, carried by contact arms 26 and 27. The current path thenproceeds through flexible braids 28 to the contact carrier strap 29. Areplaceable trip unit assembly 100, having the appropriate currentratings, and including the improved electromagnetic structure of theinstant invention in each of its phases, is inserted in the circuitbreaker. Trip unit assembly 100 includes a current carrying strap 102connected at the inward end by bolt 114 to the circuit breaker contactcarrier strap 29, and connected at its outward end to the circuitbreaker line terminal strap 21 by b'olt members 112.

Circuit breaker 10 includes a quick make-break toggle operatingmechanism generally shown as 32 for moving the contact arms 26, 27between their engaged and disengaged positions, as is more fullydiscussed in aforementioned U.S. Patent Nos. 3,302,140 and 3,319,195.For present purposes, it is sufiicient to understand that the movementof the circuit breaker to the TRIP condition of FIG. 2 results from thedisengagement of the cradle latch tip 34 from latching bracket extension101 of the trip assembly 100. Such disengagement of the latch iseffected by rotation of the trip unit assembly tripper bar 104 as aresult of actuation of the instantaneous electromagnetic trip 200, to besubsequently discussed (or, if included, the moderate overload thermaltrip 103).

The circuit breaker also includes a manual operating handle 80, whichpermits manual operation of the circuit breaker 10 to the manual OFFcontact disengaged condition. This movement is effected by moving thetoggle overcenter, without the release of cradle latch tip 34, in thewell known manner.

Although each of the three phases of the circuit breaker includes aseparate current sensing apparatus, only a single overcenter toggleoperating mechanism 32 is provided in the center phase. As is wellknown, the operation of either the manual operating handle 80, or themovement of the tripper bar 104 (common to all three phases), serves toactuate the operating mechanism 32, with such movmeent being transmittedto the other phases by virtue of tie bar 33.

Attention will now be directed to the instantaneous magnetic tripassembly, generally shown as 200, which incorporatse the improvement ofthe instant invention The trip unit assembly also includes a moderateoverload thermal trip, in the form of bimetallic element 103, in each ofthe phases connected to the current carrying strap 102 by shunt 106; asis the subject of U.S. Patent No. 3,305,653 issued Feb. 21, 1967entitled Circuit Breaker Trip Assembly With Increased Compensation forMisalignment in the name of Albert 'Strobel, based on an applicationfilled June 21, 1965 and also assigned to the assignee of the instantapplication.

The magnetic trip assembly 200 is generally of the same structure asshown in aforementioned U.S. Patent No. 3,319,195, except for themounting of the armature bias means and its interconnection to thearmature, as generally shown by the designation 250. That is, themagnetic trip assembly 200 includes a generally U-shaped magnet memberand a cooperating armature 107. The U-shaped magnet includeshorizontally disposed pole faces 111, 113, respectively, at itsuppermost extremes. The armature member 107 is horizontally disposedintermediate the plane of pole faces 111, 113 and the bottom surface 61of forwardly projecting extension 154 of the mounting bracket 150. Inits non-engaged condition, the armature member 107 is separated from thepole faces 111, 113 by an air gap separation of predetermined calibratedextent as shown by d (see FIG. 7). Upon sufficient magnetizing flux,provided by current carrying strap 10'2 flowing through the magnetmember 105, the armature member 107 is downwardly drawn towardscooperating pole faces 111, 113, as shown in the solid condition of FIG.7. This downward movement is against the biasing force provided by biasmeans 250, and will provide a negative gradient force in the uniquemanner which constitutes the subject matter of the instant invention,and will subsequently be described. I

An actuating plunger 156 is connected to the armature member 107 andmoves downwardly therewith. The actuating plunger 156 includes a tripunit actuation extension 157 adjustably threaded to the upper endthereof, which engages tripper bar extension 158 to elfect rotation ofthe tripper bar 104 and subsequent tripping of the circuit breaker uponthe downward movement of the armature member 107 towards the cooperatingpole faces 111, 113 of magnet member 105.

The actuating rod 156 also includes a calibration extension member 195,threaded at the intermediate region thereof. Calibration adjustmentmember 195 establishes the initial air gap pole separation from faces111, 113, in accordance with the rotational position of externallyaccessible calibration button 189, which is supported by bracket 191 andbiased rod 192, in the manner fully discussed in aforementioned U.S.Patent No. 3,302,140.

Reference will now be directed to the manner in which the instantinvention provides a biasing force to the armature 107. The biasingmeans is contained within a support bracket 252, which also serves asthe support for the magnet 105. This unit is appropriately maintainedwithin the trip unit assembly by fastening means which enter thethreaded openings on the magnet arms. A support bracket 254 is fixedlymounted to this assembly by screws 256 fastened to the bottom of thebracket, and extending through the body portion of magnet 105. Bracket254 extends upwardly and includes aligned apertures 258, which receivepivot pin 259. Pivot pin 259 extends through aligned apertures 261, 263at the intermediate region of a pivoted lever 260, and thereby providesa stationary pivot for the lever. I

One end of pivot .lever 260 includes aligned apertures 265, 267, whichare connected at 269 to the narrowed portion 272 of the armature stemextension 274 through a pair of rollers 269'. Armature stem extension274 has an internally threaded recess 27-6 at its upper end, whichreceives the externally threaded portion 159 of the armature stern 156,and in conjunction with nut 278, provides a firm interconnectiontherebetween. Hence, the downward movement of armature 107, which isaccompanied by similar downward movements of the armature actuating andadjustment extension 156, will similarly move the armature sternextension 274 downward. The free end of armature extension 274 includesa bulbous portion 280, which rides along the inner wall surfaces ofaperture 282 within downwardly depending portion 284 of the magnet, tothereby serve as a vertical guide.

The opposite end of the pivoted lever 260 includes aligned apertures286, 288, which receive pin member 291, with roller 292 being locatedintermediate the spaced walls of lever 260.

The pin member 291 receives one end of the armature bias spring means,illusively shown as a pair of springs 294, 296, and serves as a movablepivot therefor. The opposite ends of the springs are located withinapertures 302, 304, respectively, of the stationary support bracket 252.It should be naturally understood that a pair of springs are shown forillustrative purposes only, with more or less springs being utilized, inaccordance with the particular operating characteristics desired, in aspecific application.

A counterweight assembly generally shown as 300 is shown connected tothe opposite end of the bracket 290, via pin 305, to prevent accidentalmoving downward of the armature in the event of an apprec able shockload. The use of such a counterweight assembly may be deleted withoutdetracting from the essential spirit of the invention. It has beenfound, however, that the utilization of such a counterweight assemblywhich may be readily added to the negative gradient armature b asedstructure hereinabove described, substantially enhances the reliabilityof such an instantaneous trip mechanism when utilized in environmentsexposed to appreciable shock forces.

Reference will now be made to FIG. 7A, which shows in substantiallysimplified form, the basic operation of the negative gradient mechanismhereinabove described, in which the following corresponding partdesignations are employed: magnet member 105A; armature member 107A;armature stem extension 156A; trip unit actuating extension 157A; tripbar extension 158A; pivotal lever 260A; the point of attachment 269A tothe downwardly extending portion of the armature stem; the stationarylever pivot 259A; the stationary spring securement 302A; and the pivotalspring securement 291A. The initial position of the armature member 107Ais shown in dotted lines, with there being an air gap separation dbetween the armature 107A and the magnet pole faces. The biasing sprinfi294A will be a length L, providing a spring force of F This spring forceacts to upwardly bias the armature extension 156A (and hence thearmature 107A). This force is applied through a moment arm of length athrough the lever 260A. Hence, the effective moment of the upward forceapplied to the armature may be represented by the mathematicalrelationship- The solid line representation of FIG. 7A indicates anintermediate position of the armature 107A, as it is being drawn down bythe magnet 105A. The armature 107A is now appreciably closer to themagnetic pole faces as represented by the distance d As the armaturemoves downward, the lever 260A is rotated counterclockwise about itsstationary pivot 259A to the position shown in solid lines. Thismovement serves to traverse the end of the spring along the path indcated by the arrows 250A. The spring will now be stretched to a length Lthereby providing a greater spring force F However, by virtue of thepivoting movement of the lever 260A, this force-is applied to thearmature stern extension 156A through a small moment arm a Hence, theeffective moment of the force provided at this instant of time may berepresented by the relationship-- 8 zX z By proper design, the decreaseof the moment arm will more than compensate for the increased force ofthe spring, thereby satisfying the mathematical relationship- (3) 1 1 22 while the following condition exists It is therefore seen that acondition exists whereby,

as the armature moves closer to the magnet pole faces, the net effectiveforce applied by the bias means will be decreasing rather thanincreasing. This advantageously serves to permit an appreciable increasein the range of adjustment achieved by the initial postion of thearmature. In a typical commercial unit, built as shown in US. Patent No.3,319,195, which previously had an adjustment range of 4,000 to 8,000amperes, a comparable magnetizing circuit using the improved bias meansof the instant invention has permitted an adjustment range between 4,000to 12,000 amperes.

Further, since the moment of force opposing the downward movement of thearmature 107A decreases as the armature approaches the pole faces, therewill be a greater proportion of the force available for engaging thetrip bar extension 158A.

Referring back 0t FIG. 7, the conditions schematically shown in FIG, 7Aare represented with the dotted position showing the initial location ofthe armature prior to energi-zation, and the solid condition showing alater position of the armature. The reduction in moment arm isrepresented by a and a corresponding to the similar designations of FIG.7A.

The variation of force versus armature position of a typical assemblymanufactured in accordance with the embodiment of FIGS. 1 through 7 isgraphically shown in FIG. 12. Curve 350 shows the spring force versusarmature position. Since the tension type spring is expanding as thearmature moves closer to its cooperating pole faces, this curve, asexpected, shows an increase in spring force with decreased armatureposition. Curve 354 shows the moment of force applied to the armaturewith respect to armature position. By virtue of the reduction of themoment arm, this curve shows a condition intermediate points 355, 356,wherein the effective moment of force applied to the armature decreasesas the armature approaches its cooperating magnetic pole faces. Thus,this region has a negative force gradient at the same time that theactual spring force is shown to increase.

Reference is now made to FIGS. 8-11, which show a modified embodiment ofthe instantaneous trip assembly, to provide a lockout, with manualreset, and visual indication functions. The magnet, armature, armaturebias means and armature plunger generally correspond to that shown inconjunction with previous FIGS. 1-7, and are similarly numbered withprime designations. A manual reset and visual indicating means areprovided by the indicating lever 400. Lever 400 includes an intermediateslot 402, and is mounted to the adjustment button retaining bracket191', by virtue of rivet member 406. A distinctive color band 408 isprovided immediately below the uppermost region of the lever 400, withsuch region passing freely through slotted opening 410 of the trip unithousing cover. A bias spring 412 maintains the indicating lever 400 inthe normal position, shown in FIGS. 8 and 10.

Under normal conditions, the color band 408 is above the trip unitcover, and indicates that the instantaneous trip has not been actuated.Upon actuation of the instantaneous trip, the armature 107' movesdownward and the calibration adjustment extension 195' engages portion401 of the indicating lever, thereby moving it downward to the positionshown in FIG. 9. This downward movement serves to move the color band408 below the surface of the trip unit housing, thereby giving a visualindication of magnetic trip. The negative gradient bias means 300 ofthis embodiment is designed, as will be shown in conjunction with FIGS.11 and 13, to move overcenter during the final armature movement,thereby locking the armature in the position shown in FIG. 9. In orderto reset the breaker, it is necessary that the operator pull up on theindicating lever portion 411, forcing the armature 107' back against theovercenter locked-in arrangement of the bias means 300'.

FIG. 11 shows the manner in which the overcenter movement is achieved.At point A, corresponding to maximum armature position 107, the movableend of the spring at 259'A will exhibit a maximum downward displacementfrom the stationary pivot 261', thereby providing a maximum moment arm.As the armature moves closer to the magnetic pole face, as indicatedsuccessively by B, C, D the pivoted end of the spring 259' traverses apath, to reduce its downward vertical displacement from the pivot point261', thereby decreasing the moment arm. At point P, corresponding tovery small air gap separation, there .will be an eifective net zeroforce; however, the inertia of movement at this region and the magneticforce will keep the armature moving towards its final position, point G.At this point, the free end of the spring 259'G crosses overcenter withrespect to the pivot point 261', thereby reversing the application ofthe moment of force provided by the spring bias means, and locking thearmature in its final position. This is graphically shown in FIG. 13,where figure 360 represents the spring force. As is expected, since thespring is increasing in length as the armature approaches the magneticpole faces, there will be an increase in spring force with decreasingarmature gap. Figure 362 represents the moment of the force applied tothe armature. By virtue of the decreased moment arm, this force exhibitsa decrease as the armature approaches the air gap. At point 364,corresponding to position F of FIG. 11, there will be a net zero force.The subsequent overcenter movement of the spring provides a reversal ofthe moment, as shown by the region of the curve intermediate points 364and 366.

. Reference is now made to FIGS. 14 and 15, which show a modifiedarrangement for visually indicating the operation of the magnetic tripassembly. The instantaneous trip assembly, which is generally shown as200, includes magnet 105 and a cooperating armature 107. An actuatingplunger 156 is secured to the armature 107 and includes threaded members157, 195, corresponding in operation to identically numbered componentsof FIGS. 1-7. The instantaneous trip adjustment 500 is, however, of adifferent construction, generally conforming to that shown in US. PatentNo. 3,201,659. The armature adjustment button 501 is rotativelymaintained within bracket 502, mounted to the trip unit housing. Thebutton 501 includes a transversely extending pin 504, with a springmember 506 being located intermediate the pin 504 and the underside 505of the bracket support, thereby biasing the button 501 downward. Thebottom of the button ineludes a cam surface 510, which, upon rotation ofbutton 501 (typically by a screwdriver within slot 512), cooperates withadjustment extension 195 of the plunger 156, for establishing theinitial gap separation between the armature 107 and the pole face of themagnet 105. In accordance with my invention, the button 501 also servesas the visual indicating means of magnet actuation. When the magnet isactuated, resulting in movement of the armature 107 downward to thecondition shown in FIG. 15, button 501 moves downward under theinfluence of spring 506. As the button 501 moves down, the end 507 ofspring 506 will snap into one of the grooves 513. This prevents thebutton 501 and the armature 107 from moving upward, after the circuitbreaker trips open, thereby removing the energizing source for themagnetic trip assembly 200.

The axially downward movement of the trip adjustment button 501 servesto give the operator a visual indication of magnet actuation. In orderto reset the instantaneous feature, the operator must rotate button 501to a reset position. That is, a partial turn of button 501 will allowthe armature biasing means to force the armature 107 and the adjustmentbutton 501 upward to the position shown in FIG. 14. The operator willthen set the instantaneous trip adjustment button 501 to the desiredcalibration point, and the breaker is reset for subsequent use.

It is therefore seen that the instant invention provides anelectromagnetic device of improved operating characteristics. Inaccordance with one aspect, the armature biasing means exhibits adecrease in net effective force as the armature is drawn towards thecooperating magnetic pole faces. The various illustrative embodimentsare particularly directed to the instantaneous magnetic trip portion ofan electric circuit breaker. Where a plurality of: instantaneous magnetsare utilized, as in a multiphase unit, another aspect of the inventionis directed to a visual indicating means for apprising the operatorwhich of the electromagnetic devices has been actuated. It is to beunderstood, however, that the invention is not to be limited to suchdescribed preferred embodiments, but is defined by the appended claims.

The embodiments of the invention in which an exclusive privilege orproperty is claimed are defined as follows:

1. An electromagnetic device comprising:

a magnet means and a cooperating armature means:

a support means mounting said armature means for movement towards andaway from the pole faces of said magnet means;

bias means normally urging said armature means in a first direction awayfrom said pole faces, towards a first position whereat said armature isspaced from said pole faces;

means operable to energize said magnet means to attract said armaturemeans and move said armature means in a second direction, towards saidpole faces, to a second position;

interconnecting means connecting said bias means to said armaturesupport means, such that at least a substantial portion of the armaturemeans movement from said first position to said second position isagainst the force of said bias means;

said interconnecting means including means providing a decrease ofeffective bias force in said first direction during at least a portionof the movement of said armature means from said first position to saidsecond position.

2. An electromagnetic device as set forth in claim 1,

said bias means providing a first magnitude of force to said armaturemember, via said interconnecting means, when said armature member is atsaid first position,

said bias means providing a second magnitude of bias force to saidarmature member, via said interconnecting means, when said armaturemember is at said second position,

said second magnitude of bias force having an appreciably lowereffective force tending to urge said armature in said first direction,than said first magnitude of bias force.

3. An electromagnetic device as set forth in claim 1,

said bias means providing a first magnitude of force to said armaturemember, via said interconnecting means, when said armature member is atsaid first position,

said bias means providing a second magnitude of bias force to saidarmature member, via said interconnecting means, when said armaturemember is at said second position,

said interconnecting means providing a reversal in bias fore during thefinal movement between said first and second positions such that thefinal magnitude of bias force is applied to said armature means in amanner to urge said armature means in said second direction,

said final magnitude of reversed bias force maintaining said armaturemeans closely adjacent said magnet pole faces upon subsequent removal ofthe energizing means actuation.

4. An electromagnetic device as set forth in claim 3,

further including manual reset means for returning said armature meansto said first position against the force of said bias means, during atleast the initial portion of the reset movement.

5. An electromagnetic device as set forth in claim 1,

further including armature adjustment means for ad- 5 justing theinitial location of said armature means relative to said magnet means inthe absence of magnet energization,

said adjustment means capable of initially locating said armature meansat a third position,

said third position being intermediate said first and second position,such that said armature means is closer to the magnet pole faces at saidthird position than at said second position,

said bias means providing a first magnitude of force to said armaturemember, via said interconnecting means, when said armature member is atsaid third position,

said third magnetic of bias force having an appreciably lower effectiveforce tending to urge said armature means in said first direction thansaid first magnitude of bias force, whereby said armature means isrequired to overcome a lesser initial bias force, when moving from saidthird position towards said second position, than when moving from saidfirst position.

6. An electromagnetic device as set forth in claim 1,

said bias means being a spring means,

said interconnecting means including a variable efiective moment armintermediate said spring bias means and the application of its force tosaid armature means,

said moment arm reducing in length during at least a portion of thearmature movement in said second direction and thereby reducing theeffective force moment provided by said bias spring.

7. An electromagnetic device as set forth in claim 3,

said bias means being a spring means,

said interconnecting means including a variable effective moment armintermediate said spring bias means and the application of its force tosaid armature means,

said moment arm reducing in length during at least a portion of thearmature movement in said second direction and thereby reducing theeffective force moment provided by said bias spring,

the moment of said second magnitude of force reversing during theterminating portion of armature movement toward said second position.

8. An electromagnetic device as set forth in claim 1,

said bias meansbeing a spring means,

said spring means having first and second ends,

a first stationary point for said first end,

a second movable pivot point for said second end,

said second pivot point operatively connected to said armature means andmoving, simultaneously with armature movement, relative to said firstpoint,

the relative location of said first and second points establishingtheeifective moment arm of the biasing force applied by said springmeans to said armature means,

said moment arm being reduced during at least a predetermined portion ofthe path of armature movement in said second direction.

9. An electromagnetic device as set forth in claim 8,

said spring force increasing during said predetermined portion ofarmature movement,

the reduction of moment arm compensating for the increased spring force,thereby providing a decreased effective moment of force.

10. An electromagnetic device as set forth in claim 8,-

the movement of said armature means satisfying the relationships,

1 X 1 z X 2 and F 1 2 where F =the spring force when the armature meansis at said first position,

a =the moment arm applying F to the armature means,

F =the spring force during the predetermined portion of the path ofarmature movement, I

a =the moment arm applying F to the armature means.

11. An electromagnetic device as set forth in claim 8,

said second pivot point crossing overcenter, relative to said firstpivot point, during the final movement of said armature means towardsits final position closely adjacent said magnet pole faces,

said overcenter movement reversing the application of the moment offorce provided by said spring means, and locking said armature means insaid final position.

12. A circuit breaker comprising at least one pair of cooperatingcontacts,

contact operating means operable to move said contacts between anengaged and disengaged position;

latch means in cooperation with said operating means operable tomaintain said contacts in their engaged position under normal loadconditions;

a trip unit including current sensing means operatively responsive tothe current flow through the circuit, and including means operable torelease said latch means responsive to predetermined overloadconditions,

said current sensing means including a magnetic trip assembly havingcooperating magnet and armature means,

support means mounting said armature means for movement towards and awayfrom the pole faces of said magnet means;

bias means normally urging said armature means in a first direction awayfrom said pole faces, towards a first position whereat said armaturemeans is spaced from said pole faces;

means operable to energize said magnet means to attract said armaturemeans and move said armature means in a seconddirection, towards saidpole faces, to a second position;

interconnecting means connecting said bias means to said armaturesupport means, such that at least a substantial portion of the armaturemeans movement from said first position to said second position isagainst the force of said bias means;

said interconnecting means including means providing a decrease ofeffective bias force in said first direction during at least a portionof the movement of said armature means from said first position to saidsecond position.

13. A circuit breaker as set forth in claim 12,

said bias means providing a first magnitude of force to said armaturemember, via said interconnecting means, when said armature member is atsaid first position,

said bias means providing a second magnitude of bias force to saidarmature member, via said interconnecting means, when said armaturemember is at said second position,

said second magnitude of bias force having an appreciably lowerelfective force tending to urge said armature means in said firstdirection, than said first magnitude of bias force.

14. A circuit breaker as set forth in claim 12,

said bias means providing a first magnitude of force to said armaturemember, via said interconnecting means, when said armature member is atsaid first position,

said bias means providing a second magnitude of bias force to saidarmature member, via said interconnecting means, when said armaturemember is at said second position,

said interconnecting means providing a reversal in bias force during thefinal movement between said first and second positions such that thefinal magnitude of bias force is applied to said armature means in amanner to urge said armature means in said second direction,

said final magnitude of reversed bias force maintaining said-armaturemeans closely adjacent said magnet pole. faces upon the subsequentclearing up of said predetermined overload condition.

15. A circuit breaker as set forth in claim 12,

counterbalance means acting on said interconnecting means in associationwith said bias means to counteract the shock induced movement of saidarmature means towards said pole faces. I

16. A'circuit breaker as set forth in claim 12, further including; i

armature adjustment means for adjusting the initial location of saidarmature means relative to said magnet means in the absence of magnetenergization,

said adjustment means capable of initially locating said ar-mature meansat a third position,

said third position being intermediate said first and second position,such that said armature means is closer to the magnet pole faces at saidthird position than at said second position,

said bias means providing a first magnitude of force to to said armaturemember, via said interconnecting means, when said armature member is atsaid first position,

said bias means providing a third magnitude of bias force to saidarmature member, via said interconnecting means, when said armaturemember is at said third position,

said third magnitude of bias force having an appreciably lower effectiveforce tending to urge said armature means in said first direction, thansaid first magnitude of bias force, whereby said armature means isrequired to overcome a lesser initial bias force, when moving from saidthird position towards said second position, than when moving from saidfirst position.

17. A circuit breaker as set forth in claim 12,

said bias means being a spring means,

said interconnecting means including a variable effective moment armintermediate said spring bias means and the application of its force tosaid armature means,

said moment arm reducing at least a portion of the armature movement insaid second direction and thereby reducing the effective force momentprovided by said bias spring.

18. A circuit breaker as set forth in claim 12,

said bias means being a spring means,

said spring means having first and second ends,

a first stationary point for said first end, i

a second movable pivot point for said second end,

said second pivot point operatively connected'to said armature means andmoving, simultaneously with armature movement, relative to said firstpoint,

the relative location of said first and second points establishing theeffective moment arm of the biasing force applied by said spring meansto said armature means,

said moment arm being reduced during at least a predetermined portion ofthe path of armature movement in said second direction.

19. A circuit breaker as set forth in claim 18,

the movement of said armature means satisfying the relationships,

and

where F =the spring force when the armature means is at said firstposition,

a =the moment arm applying F to the armature means,

F =the spring force during the predetermined portion of the path ofarmature movement,

a =the moment arm applying F to the armature means.

20. A circuit breaker as set forth in claim 18,

counterbalance means acting on said interconnecting means in associationwith said bias means to couteract the shock induced movement of saidarmature means towards said pole faces,

said counterbalance means provided by a weight op eratively applied tosaid second pivot point.

21. A circuit breaker as set forth in claim 12,

said magnet or a generally U-shaped configuration,

including space-separated arms joined by a body portion, said bodyportion disposed generally horizont-ally, and mounted at the lowerregion of said trip unit, with said arms vertically extending upwardlytherefrom, the uppermost extremes of said arms ineluding said pole facesdisposed in a generally horizontal plane, vertically displaced upwardsfrom said body portion, said armature member horizontally extendingparallel to the plane of said pole faces, and bridging the spaceseparation between the arms thereof, said armature member first positionbeing above said pole faces, and separated therefrom by a predeterminedgap with said first position corresponding to the disengaged conditionof the magnetic trip assembly, said armature means in contact with saidpole faces at said second position, said second posi tion correspondingto the engaged condition of the magnetic trip assembly, said magnetenergizing means for moving said armature in said second directiondownwardly between said first and second positions corresponding to apredetermined overload condition, an actuating rod mounted to saidarmature, and including a first portion upwardly extending therefrom ina generally vertical direction, a trip unit actuating extension mountedto said rod for movement therewith responsive to downward movement ofsaid armature towards its engaged condition, means operativelyconnecting said actuating extension to said contact operating latchmeans, for release of said latch means responsive to downward movementof said actuating rod, said bias means upwardly biasing said armature insaid first direction towards its first position, said actuating rodincluding a second portion downwardly extending towards said magnet bodyportion,

said interconnecting means including a pivoted lever having anintermediate stationary pivot and opposed first and second ends,

said first end of said lever connected to said second portion of theactuating rod,

said bias means including elongated spring means having first and secondends,

said first spring end connected to a stationary member,

said second spring end connected to said second end of said lever,

the vertical displacement between said lever second end and intermediatestationary pivot establishing the ef- H 15 I I fective moment arm of thespring bias force applied to said armature, 1

said second end normally located a firstdistance below said stationarypivot when saidarmature means is at said first position, t

the downward movement of said armature means towards said secondposition moving saidv second lever end upward towards said intermediatestationary pivot to reduce the effective moment of the spring forceapplied to said armature means.

22. A circuit breaker as set forth in claim 21,

said spring force increasing while said effective moment arm decreases,with their product decreasing to thereby effectively reduce themoment'of spring bias force as said armature means moves towards themagnetic pole faces.

23. A circuit breaker as set forth in claim 21,

said second lever end moving overcenter above said 16 I intermediatestationary pivot when said armature means is in saidv second position,andfthereby effecting a reversal in the direction of the spring biasmoment to locksaid armature meansin said second portion.

7 References Cited UNITED STATES PATENTS BERNARD A. GILHEANY, PrimaryExaminer 1 H.. BROOME, Assistant Examiner Us; 01. X.R. 335-4 UNITEDSTATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 505 ,626Dated 7 April 1970 Howard R. Shaffer Inventor (s) It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 10, line 75 change "fore" to force Column 11, line 29 change"magnetic" to magnitude Column 13, line 41 delete "to" I Column 14, line22 change "couter-" to counter- Column 14, line 28 change "or" to havingSlGNEDAiW SEALED 00'1'13 mm 1:. sum, .13. Am 0m Oomisaiom of PatentsFORM F'O-1U5Dl 0-69) LJSCOMM-DC ooan-Pco 9 us GOVIRHNENY PRINTING OFICE9i! D-!ii-ll4

